linux-kernel - Re: [PATCH v2 10/11] KVM: SVM: implement support for vNMI

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Date:   Sat, 28 Jan 2023 01:10:18 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Maxim Levitsky <mlevitsk@...hat.com>
Cc:     kvm@...r.kernel.org, Sandipan Das <sandipan.das@....com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Jim Mattson <jmattson@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Borislav Petkov <bp@...en8.de>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Daniel Sneddon <daniel.sneddon@...ux.intel.com>,
        Jiaxi Chen <jiaxi.chen@...ux.intel.com>,
        Babu Moger <babu.moger@....com>, linux-kernel@...r.kernel.org,
        Jing Liu <jing2.liu@...el.com>,
        Wyes Karny <wyes.karny@....com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        Santosh Shukla <santosh.shukla@....com>
Subject: Re: [PATCH v2 10/11] KVM: SVM: implement support for vNMI

On Tue, Nov 29, 2022, Maxim Levitsky wrote:
> This patch implements support for injecting pending
> NMIs via the .kvm_x86_set_hw_nmi_pending using new AMD's vNMI
> feature.
> 
> Note that the vNMI can't cause a VM exit, which is needed
> when a nested guest intercepts NMIs.
> 
> Therefore to avoid breaking nesting, the vNMI is inhibited while
> a nested guest is running and instead, the legacy NMI window
> detection and delivery method is used.
> 
> While it is possible to passthrough the vNMI if a nested guest
> doesn't intercept NMIs, such usage is very uncommon, and it's
> not worth to optimize for.
> 
> Signed-off-by: Santosh Shukla <santosh.shukla@....com>
> Signed-off-by: Maxim Levitsky <mlevitsk@...hat.com>
> ---
>  arch/x86/kvm/svm/nested.c |  42 +++++++++++++++
>  arch/x86/kvm/svm/svm.c    | 111 ++++++++++++++++++++++++++++++--------
>  arch/x86/kvm/svm/svm.h    |  10 ++++
>  3 files changed, 140 insertions(+), 23 deletions(-)
> 
> diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
> index e891318595113e..5bea672bf8b12d 100644
> --- a/arch/x86/kvm/svm/nested.c
> +++ b/arch/x86/kvm/svm/nested.c
> @@ -623,6 +623,42 @@ static bool is_evtinj_nmi(u32 evtinj)
>  	return type == SVM_EVTINJ_TYPE_NMI;
>  }
>  
> +static void nested_svm_save_vnmi(struct vcpu_svm *svm)
> +{
> +	struct vmcb *vmcb01 = svm->vmcb01.ptr;
> +
> +	/*
> +	 * Copy the vNMI state back to software NMI tracking state
> +	 * for the duration of the nested run
> +	 */
> +

Unecessary newline.

> +	svm->nmi_masked = vmcb01->control.int_ctl & V_NMI_MASK;
> +	svm->vcpu.arch.nmi_pending += vmcb01->control.int_ctl & V_NMI_PENDING;
> +}
> +
> +static void nested_svm_restore_vnmi(struct vcpu_svm *svm)
> +{
> +	struct kvm_vcpu *vcpu = &svm->vcpu;
> +	struct vmcb *vmcb01 = svm->vmcb01.ptr;
> +
> +	/*
> +	 * Restore the vNMI state from the software NMI tracking state
> +	 * after a nested run
> +	 */
> +

Unnecessary newline.

> +	if (svm->nmi_masked)
> +		vmcb01->control.int_ctl |= V_NMI_MASK;
> +	else
> +		vmcb01->control.int_ctl &= ~V_NMI_MASK;
> +
> +	if (vcpu->arch.nmi_pending) {
> +		vcpu->arch.nmi_pending--;
> +		vmcb01->control.int_ctl |= V_NMI_PENDING;
> +	} else
> +		vmcb01->control.int_ctl &= ~V_NMI_PENDING;

Needs curly braces.